The Meaning of the Atlantic : 63 



though the ocean does exert a temperating influence even along the 

 Atlantic seaboard, and the deep indentation in the continent created 

 by the combined effects of the Caribbean Sea and the Gulf of Mexico 

 influences the southern part of the United States. That the presence 

 of the Atlantic can influence the temperature and climate even in 

 cases where the prevailing winds blow from the land to the ocean 

 does not seem to be very well understood. 



Rainfall and Moisture: The water that the ocean is continually 

 receiving through the flow of rivers from the continents must be 

 restored to the continents again in order to preserve the cycle and 

 the plans of nature. This is taken care of by evaporation of the water 

 along the shores of the continents and also in the open sea. In gen- 

 eral, what we have said about temperature control applies also to 

 moisture control. 



The Atlantic with all its seas, gulfs and other ramifications is con- 

 tinually renewing and refreshing the moisture content of the air so 

 that the lakes and rivers may be supplied through the fall of rain 

 and snow, fogs and mists and other forms of water transport and 

 precipitation. It is worth special mention that the function of the 

 Gulf Stream is not only to keep the waters of northern Europe 

 warm and the harbors open but also to keep the climate wet. At 

 first we might suppose that the most rapid rate of evaporation took 

 place where the sun was usually shining and the air was generally 

 warm and that evaporation was generally low or negligible in tem- 

 perate and northern climates. 



The story is not quite as simple as this. A study has been made 

 and a curve drawn to show the rate of evaporation from the open 

 Atlantic all the way from 50° north to 50° south. The highest rate 

 of evaporation comes in one band a little north of the equator and 

 in another band a little south of it with a slight depression at the 

 equator itself. It is a minor but interesting point to note that the sec- 

 tion in the tropics seems to reflect the fact that wind, as well as 

 warmth, adds to the rate of evaporation; therefore, the areas of max- 

 imum evaporation are in the zone of the trade winds and not at the 

 equator which is marked by the doldrums — a region of calm and fit- 

 ful winds. 



The important point however is that the total evaporation in the 

 tropics is much less than we might expect and evaporation in the 

 middle and higher latitudes is much greater. The reason for this is 

 that a high rate of evaporation takes place whenever the water is 

 warm and the air above it relatively cold. In the tropics, of course, 



